Making windows transparent in 12.10 with Gallium 0.4 on AMD CEDAR

Question

I'm trying to make my gvim window partially transparent. I've tried ccsm and transset, but neither work with the open source video drivers for AMD. Both methods do work with the proprietary drivers.

When a run transset from the command line and select a window, it says that it has set the transparency to 75%, but there is no visual difference.

My video card is a PowerColor ATI Radeon HD5450 512 MB DDR3, and I've verified that Unity is in 3D mode.

>/usr/lib/nux/unity_support_test -p
OpenGL vendor string:   X.Org
OpenGL renderer string: Gallium 0.4 on AMD CEDAR
OpenGL version string:  2.1 Mesa 9.0

Not software rendered:    yes
Not blacklisted:          yes
GLX fbconfig:             yes
GLX texture from pixmap:  yes
GL npot or rect textures: yes
GL vertex program:        yes
GL fragment program:      yes
GL vertex buffer object:  yes
GL framebuffer object:    yes
GL version is 1.4+:       yes

Unity 3D supported:       yes